Treatment of wells



Patented Apr. 23, 194$ ,uaas

TREATMENT OF WELLS Sterling P. Hart, Long Beach, Calif., assignor to The Texas Company, New York, N. Y., a corporation of Delaware No Drawing.

Application August 31 1938,

Serial No. 227,504

4 Claims.

This invention relates to the treatment of wells,

and more particularly to a method adapted to rendering oil wells more productive.

More specifically my invention relates to a 6. method of removing from the face of an oil sand adjacent a well bore caked drilling mud which may be all and wax saturated, whereby an unretarded flow of oil from the oil sand into the hole is made possible. I accomplish this by treating the well bore with an alkaline solution of an alkali metal perborate.

Drilling muds are almost universally used in the drilling of wells employed for tapping underground collections of oil, gases, brines and water. These muds fulfill various functions, the most important of which are to assist in the removal of cuttings from the well, to seal oil gas pockets which may be encountered at various levels, and to lubricate the drilling tools and the drill pipes 20 which carry the tools.

Drilling muds are essentially mixtures of finely divided solids such as clay with water, usually so compounded that they weigh from 8 to 12 pounds per gallon. Whenever it is found necessary to 25 increase the specific gravity of a particular mud it is customary to add thereto finely divided materials which have a high specific gravity, such for example as barytes, litharge, and the like.

When drilling with a drilling mud, the mud is to circulated to the locus of drilling through the drill pipe and then upwardly to the surface in the annular space between the hole and the drill pipe. During the drilling operation the solid phase of the drilling fluid or mud compacts on the :5 face of the well bore in the form of a filter cake, or mud sheath. The mud sheaths formed on the walls of the well bore in this way prevent the loss of drilling mud into the formations penetrated by the well bore, and because of their 0 plastering action supply a certain amount of mechanical strength to the walls of the hole. The mud sheaths however have the. disadvantage of obstructing the free passage of oil into the well from an oil sand.

When a mud sheath covers a high pressure gas sand the flow from the sand to the well bore usually is readily established and usually becomes so violent that the sheath is quickly disintegrated and swept off the face of the wall. Where, however, the mud sheath covers a low pressure oil sand, the pressure may be insufi'icient to rupture the mud sheath and production from the sand may never be established. Assuming however that production from a low pressure sand is established through a mud sheath, the sheath becomes saturated with oil, wax and asphaltic material, with the result that the oil production is seriously diminished.

From the foregoing it can be seen that the effective removal of mud sheaths, whether fresh or oil soaked, is an important consideration. The importance of the problem of removing mud sheaths is best judged by the number of methods of removal which have been proposed, these methods being classified either as mechanical or chemical. The former include methods such as washing and swabbing and generally any me chanical method adapted for removing the mud sheath, whereas the latter include treatments with acids, alkalis and solvents. Although a small measure of success has attended the use of both types of treatment, the fact that no one method has achieved wide recognition indicates that no method has been universally successful.

I have discovered a chemical wash solution which is more effective for disintegrating mud sheaths than any proposed to date, this chemical solution being equally as effective on fresh mud sheaths as on mud sheaths which have become permeated with oil, wax or asphalt.

My invention contemplates washing the well bore with an alkaline solution of an alkali metal perborate, whereby the mud sheath lining the walls 'of the uncased hole becomes disintegrated and is easily washed out of the hole. In the use of this chemical solution it is preferable that the same be applied with mechanical agitation, not only to capitalize on the disintegrating effect resulting from violent agitation but also to prevent the establishment of equilibrium conditions at the face of the mud sheath.

In order that those skilled in the art may fully understand my invention, I give herewith an example of a treating solution prepared in accordance with my invention. This solution is prepared by dissolving 40 pounds of solid caustic soda in 50 gallons of water, and then cooling the solution to atmospheric temperature. When the solution has been cooled there are added to the caustic solution 30 pounds of sodium perborate. It is to be understood that the amounts of caustic soda and sodium perborate used may vary over wide ranges, for example the water solution may be saturated with respect to one or both of the ingredient chemicals, or the water solution may be more dilute than the solution shown in the example, although for the usual type of mud sheath the example given will be found highly effective.

Where the filter cake is extremely impermeable to water it may be advantageous to incorporate in the water solution a small amount of a wetting agent which is compatible with the caustic and the sodium perborate. For this purpose an alkali metal soap of a fatty acid, of a rosin acid, or a naphthenic acid may be used. I contemplate too the use of salts of sulphonated high molecular weight alcohols, as well as small quantities of saturated aliphatic alcohols containing from six to twelve carbon atoms, and in fact any chemical compound which has the property of substantially reducing the surface tension of the alkaline solutions of alkali metal perborates which form the basis of my invention.

Obviously many modifications and variations of the invention as herelnbefore set forth may be made without departing from the spirit and scope thereof, and only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. The method of removing a mud sheath from a well bore which comprises subjecting the mud sheath to the action of a reagent comprising an aqueous solution of an alkali metal perborate.

2. The method of removing a mud sheath from a well bore which comprises subjecting the mud sheath to the action of a solution in water of an alkali metal hydroxide and an alkali metal perborate.

3. The method of removing a mud sheath from a well bore which comprises subjecting the mud sheath to the action of a water solution of sodium hydroxide and sodium perborate.

4. The method of treating a well to remove incrustations from the well bore, which comprises introducing into the well and into contact with the said incrustations on the well bore an aqueous alkaline solution of an alkali metal perborate.

STERLING P. HART. 

